1. Field of the invention:
The present invention relates to a process for preparing organic monomolecular films, particularly to a process for the lamination of organic monomolecular films having two or more organic monomolecular film layers. Also, the present invention relates to a chemical adsorbent used for this process.
2. Description of the prior art:
An organic monomolecular film has been utilized in various devices for the purpose of protecting their surface, providing them with excellent lubricant properties or water repellent properties. Also, it is used as a film having a molecular orientation used in liquid crystals. For the formation of the organic monomolecular film, the Langmuir-Blodgett (LB) technique is well known. According to the LB technique, the organic monomolecular film can be formed as follows. First, straight chain hydrocarbon molecules having a hydrophilic group at one molecular end and a hydrophobic group at the other end spread on the surface of the water. The hydrophilic groups direct toward the depth of the water, whereas the hydrophobic groups direct toward the surface of the water. Next, when the whole area of the hydrocarbon molecules are narrowed with a barrier, the area per one hydrocarbon molecule becomes smaller. The hydrocarbon molecule chains are then packed closely together to form a monomolecular film with each molecular chain being directed at a right angle to the surface of the water. The resulting monomolecular film is attached to the surface of a base plate to form a monomolecular film layer. Also, the lamination of monomolecular films can be formed by laminating one or more monomolecular films on the base plate.
The monomolecular film formed by the LB technique mentioned above is attached to the base plate by van der Waals force, or ionic bonding strength. Also, when a lamination of monomolecular films having two or more layers is formed, monomolecular films are bound together by van der Waals force, or ionic bonding strength. However, the binding energy of these bindings between the base plate and the monomolecular film, or between each monomolecular films is so low that the monomolecular film or the lamination cannot be attached to the base plate tightly. Therefore, the monomolecular film or the lamination is susceptible to peeling or dissolving into solvent when the base plate is processed.
To solve these problems, a chemical adsorption technique has been proposed for preparing a monomolecular film. In this technique, a straight chain hydrocarbon having chlorosilane group at one molecular end is used as a chemical adsorbent. When the chemical adsorbent is applied to the surface of a base plate having a hydroxyl group, the chlorosilane group reacts with the hydroxyl group for the elimination of hydrogen chloride. Thus, the chemical adsorbent is bound chemically to the base plate through --Si--O-- bond to form a monomolecular film on the base plate. Because the monomolecular film formed by this technique is bound chemically to the base plate, it will not peel even though the base plate is processed.
However, only a few technques are known for the formation of two or more monomolecular film layers which do not readily peel. The following illustrates one of the chemical adsorption techniques for laminating two monomolecular films. A first monomolecular film is formed on a base plate by using a hydrocarbon molecule having a double bond at the molecular end. The monomolecular film is then irradiated with an electron beam. The irradiation of electron beam under N.sub.2 or O.sub.2 atmosphere changes the double bond to --NH.sub.2 group or --OH group, respectively. Next, a straight chain hydrocarbon having chlorosilane group such as --SiCl.sub.3 is applied to the irradiated monomolecular film. The straight chain hydrocarbon molecule is bound to the hydrocarbon molecule of the first monomolecular film by the reaction of the chlorosilane group with --NH.sub.2 or --OH group, and therefore a lamination of monomolecular films having two monomolecular film layers can be formed. However, because the irradiation of electron beams may cause side reactions such as crosslinking reaction between each hydrocarbon molecules of the first monomolecular film formed on the base plate, a lamination of monomolecular films with desirable properties cannot be obtained by this technique.
A lamination of monomolecular films is also formed by the following chemical adsorption technique. A first monomolecular film is formed on a base plate by the same procedure as described above using hydrocarbon molecules, and then the first monomolecular film reacts with diborane instead of irradiating with an electron beam. The double bond present in the first monomolecular film is converted into a hydroxyl group by the reaction of diborane. Then, by the same procedure as described above, the hydroxyl group reacts with the chlorosilane group of another hydrocarbon molecule to form a lamination of monomolecular films. However, because diborane reacts explosively when it comes into contact with wet air, it is difficult to handle diborane, and dangerous to carry out this technique.